In order to detect the rotational phase of a rotating body, a recessed reference mark that can be detected with an electromagnetic wave such as light is provided on the surface of the rotating body in some cases. However, providing such a recessed reference mark will result in non-uniform weight balance of the rotating body the rotating direction. As a result, an imbalance occurs in the rotating body, which may cause the rotating body to vibrate.
In such a case, the amount of imbalance in the rotating body can be reduced by the imbalance correcting method described in Patent Document 1, for example. In the method described in Patent Document 1, first, the amount of imbalance in a rotating body is measured, and a section of the rotating body is cut and removed based on the measurement result so as to cancel the imbalance. In particular, the method of Patent Document 1 claims to effectively reduce the amount of imbalance by cutting and removing two or more sections of the rotating body when removal of one section is not sufficient to cancel the imbalance.